The present invention relates to a friction stir welding machine. More particularly, the present invention relates to a spindle for a friction stir welding machine.
Friction stir welding is a process of welding component parts together using friction heat generated at a welding joint to form a plasticized region that solidifies to join workpiece sections. Welding is performed by inserting a probe into a joint between the workpiece sections. The probe includes a pin that is inserted into the joint and a shoulder, which is urged against the surfaces of the workpieces. The pin and shoulder spin together to generate friction heat to form the plasticized region along the joint for welding operation.
Various parameters must be controlled in order to form a quality weld. One of the more critical parameters is the depth of the probe. As is known in the art, the depth of the probe can be controlled using either position or load control. Position control is generally difficult because of the high loads present on the spindle during the welding process. In particular, the spindle and the probe are under a considerable load, which will cause flexure and bending in various components thereof, which in turn will affect the accuracy of the position measurement. In view that the spindle must also operate in multiple degrees of freedom, the individual loading on the components of the spindle can vary depending on the position of the spindle in space. In addition, thermal expansion of the probe must also be taken into account in position control.
Load control has also been used to control the welding process. Load control requires measuring the normal load or force on the welding probe (i.e. the force coincident with the spinning axis of the probe). Prior art techniques for load control require supporting the whole spindle assembly on one or more load cells. Since the spindle assembly is commonly quite heavy, the load cells used must be of large capacity, which increases the cost of the machine and as well as generally sacrificing accuracy.
One aspect of the present invention is a friction stir welding spindle that includes a support having a center bore. A spindle shaft is adapted to support a stir welding tool and extends within the bore. A bearing assembly allows simultaneous rotational and axial displacement of spindle shaft in the bore relative to the support. A sensing device is adapted to provide an output signal indicative of at least one of a force coincident with axial displacement of the spindle shaft and the axial position of the spindle shaft.
In another aspect of the present invention, a portion of the spindle shaft cooperates with the support, forming an actuator adapted to cause axial displacement of the spindle shaft relative to the support. For instance, the actuator can be fluidly operated from pressurized fluid wherein the portion of the spindle shaft cooperates with the inner surface of the bore to form pressurizable chambers which, when pressurized, will cause axial displacement of the spindle shaft relative to the support. Pneumatic or hydraulic operation can be employed. In yet other embodiments, the spindle shaft and the support can cooperate magnetically to form an actuator.